Abstract
Interspecific differences in morphology, biomass allocation and phenotypic plasticity along an experimental irradiance gradient and two contrasting water regimes were studied for eight Mediterranean woody species at the seedling stage; a critical demographic stage in Mediterranean plant communities. We tested whether species variation in these traits can explain previously reported interspecific differences in performance under shade and drought. Four irradiance levels (1%, 6%, 20% and 100% of full sunlight) and two water regimes (well watered and water-stressed conditions) in 6% and 100% irradiance levels were established. Quercus species exhibited the largest seeds, the highest total dry mass and also the highest root-shoot ratio, but their leaf mass fraction (LMF) and leaf area ratio (LAR) were low. Pistacia terebinthus, and Arbutus unedo exhibited the opposite traits. From those traits that correlated with seed size only LAR resulted significantly linked to survival in deep shade. None of the traits studied correlated with survival under water-stressed conditions. Overall phenotypic plasticity was negatively correlated with survival in deep shade but no correlation was found with survival under water-stressed conditions. Our results highlight the importance of low LAR and low phenotypic plasticity as potential determinants of enhanced performance under shade during the very early seedling stages of Mediterranean woody species. Low LAR was also positively correlated with seed size and consequently, its relationship with enhanced performance under shade might change at later life stages of the plant when seed reserves are no longer available.
Résumé
Les différences interspécifiques de morphologie, d’allocation de biomasse et de plasticité phénotypique ont été étudiées pour des semis de huit espèces ligneuses méditerranéennes sous un gradient d’ombrage et soumis à deux régimes d’alimentation hydrique. Le stade semis est un stade critique pour la démographie des communautés végétales méditerranéennes. Nous avons testé l’hypothèse que des différences dans ces traits pouvaient expliquer les différences inter-spécifiques de performances souvent décrites sous ombrage et sous sécheresse. Nous avons imposé quatre niveaux d’ombrage (1 %, 6 %, 20 % and 100 % du rayonnement incident) et deux régimes hydriques (irrigation abondante et déficit hydrique pour les traitements 6 % et 100 %). Les chênes présentaient les graines les plus grosses, la plus forte biomasse et également le rapport racine/parties aériennes le plus élevé, mais leurs rapports (biomasse foliaire/biomasse totale) et (surface foliaire/biomasse totale) (LAR) étaient faibles. Pistacia terebinthus, et Arbutus unedo présentaient des caractéristiques opposées. Parmi ces traits liés à la taille des graines, seul LAR était fortement corrélé à la survie sous ombre forte. Aucun des traits mesurés n’était corrélé à la survie sous sécheresse. Le degré de plasticité phénotypique était corrélé négativement avec la survie sous ombre forte, mais aucune corrélation n’a pu être détectée avec la survie sous sécheresse. Ces résultats soulignent l’importance d’un LAR faible et d’une faible plasticité phénotypique comme déterminants d’une survie sous fort ombrage pendant les tous premiers stades de développement des semis de ligneux méditerranéens. De faibles valeurs de LAR étaient également associées à de fortes biomasses initiales des graines; son effet sur la performance des semis à l’ombre risque de ce fait de disparaître lors des stades de développement ultérieurs quand les réserves des graines sont épuisées.
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Sánchez-Gómez, D., Zavala, M.A. & Valladares, F. Functional traits and plasticity linked to seedlings’ performance under shade and drought in Mediterranean woody species. Ann. For. Sci. 65, 311 (2008). https://doi.org/10.1051/forest:2008004
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DOI: https://doi.org/10.1051/forest:2008004